I. Field of the Invention
The present invention relates generally to gerotor pumps, and more particularly to improved gerotor pumps wherein an outer rotor of gerotor sets utilized therein is enabled for finding its own eccentricity offset axis whereat it is supported mechanically via forcibly meshing with the inner rotor at the gerotor set in-mesh position and otherwise in a nominally hydrostatically balanced manner.
I. Description of the Prior Art
Gerotor pumps are most conveniently designed around commercially available gerotor gear sets (hereinafter simply “gerotor sets”) such as those manufactured by Nichols Portland of Portland, ME. Such gerotor sets comprise an inner rotor having N outwardly extending lobes with N approximately circularly shaped grooves therebetween (i.e., with N typically having values of 4, 6, 8 or 10) in mesh with an eccentrically disposed outer rotor comprising N+1 inwardly extending circularly shaped elements. Often the inner rotor is mounted upon and directly driven by the drive shaft of a prime mover such as an electric motor. The eccentrically disposed outer rotor is then driven by the inner rotor via meshing of the outwardly and inwardly extending lobes then instantly located nominally nearest an “in-mesh” position. This meshing contact occurs with near zero relative velocity between inner and outer rotors in the region of the in-mesh position while a maximum relative velocity between tips of the outwardly extending lobes of the inner rotor and the inwardly extending lobes of the outer rotor occurs at the opposite or out-of-mesh position along an eccentricity axis.
Present art gerotor pumps typically comprise a fixedly positioned eccentric gerotor pocket within which the outer rotor is supported by a hydrodynamic bearing formed in the space between the eccentric gerotor pocket and the outer rotor. In most gerotor pumps the gerotor pocket is simply formed as part of the pump housing and then completed by a cover plate wherein inner surfaces of the gerotor pocket and cover plate serve as first and second sides of a gerotor cavity. The bore of the eccentric gerotor cavity is formed about a preferred eccentricity offset rotation axis located along a preferred eccentricity axis at a distance nominally equal to a gear addendum. Axially oriented symmetrical fluid commutation ports are formed in either or both of the first and second sides of the gerotor cavity to either side of the preferred eccentricity axis and are fluidly coupled to housing ports.
In operation, fluid is conveyed from the inlet fluid commutation port to inlet side ones of N+1 pumping chambers formed between the outwardly and inwardly extending lobes and elements as they move out of mesh on the inlet side, and then out the outlet fluid commutation port via outlet side ones of the N+1 pumping chambers as they move back toward mesh on the outlet side. The pumping chambers are formed between N nominal line seals provided by the mesh of the outwardly and inwardly extending lobes and elements and an additional nominal line seal between one inwardly extending element and a juxtaposed one of the grooves of the inner rotor nearest the “in-mesh” position. Thus, fluid entering via the inlet fluid commutation port is conveyed to the outlet fluid commutation port at a pressure value determined by the system load via each of the sequentially moving ones of the N+1 pumping chambers. Interestingly, the shaft must rotate (N+1)/N revolutions for a complete cycle of any of the N+1 pumping chambers.
Transverse or lateral loading between the inner and outer rotors is nominally generated by the product of the difference between the output and input pressures, and the net transverse plan area between instant ones of the sealing lines formed nearest to the “in” and “out” of mesh positions. Normally the outer rotor is directly supported by the hydrodynamic bearing formed between it and the eccentric housing bore as described above. Alternately, a needle bearing could be used to support the outer rotor for a gerotor pump that rotates at too low a speed to generate sufficient hydrodynamic bearing support.
As noted above, prior art gerotor pumps utilize fixedly positioned eccentric gerotor pockets in concert with meshing gerotor sets. As a result of this they are mechanically over constrained whereby it is impractical to utilize closely fitting inner and outer rotors such as are required for generating high output pressure values. And even with the commonly available relatively loose fitting gerotor sets (e.g., with perhaps 0.003 in. dimetral clearance), the actual driving contact position of mesh between inner and outer rotors is indeterminate. Thus, there is considerable variation in frictional rubbing and wear between and of lobes of supposedly identical gerotor pumps.
This concern was addressed in the incorporated '812 patent application wherein gerotor pumps having an additional degree of freedom and thus permitting their outer rotors to find their own optimum centers of rotation under all conditions of loading and shaft deflection were disclosed. Particularly in the case of disclosed gerotor pumps comprising floating rings for locating and supporting the outer rotors, the additional degree of freedom also allowed operation at relatively high output pressure values via utilizing precision formed gerotor sets such as those described in connection with FIGS. 33 through 43 of the incorporated '812 patent application. However, the gerotor pumps disclosed therein continued to utilize gerotor sets wherein lobe-to-lobe contact was possible at positions other than at line seals nearest the in-mesh position (i.e., including the out-of-mesh position). Furthermore, imprecisely defined hydrodynamic bearing supported forces were still present in those gerotor pumps. It would be desirable to provide gerotor pumps comprising floating rings wherein these remaining concerns have been addressed.
The primary object of the present invention, then, is to provide gerotor pumps wherein gerotor sets are forcibly held in mesh at the in-mesh position whereby the outer rotors are mechanically driven by the inner rotors under nominally zero differential velocity meshing conditions and thereby in a substantially friction- and wear-free manner.